Radio signal enhancing frequency conversion method



Aug. 26, 1952 J. c. MYERS 2,608,650

' RADIO SIGNAL ENHANCING FREQUENCY CONVERSION METHOD Filed Sept. 1, 1945 6 r 5 f -l- 57 INPl/T SIG/VAL f LOCAL 030. F

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dac ob Myer-s Patented Aug. 26, 1952 JRADIOSIGNAL'ENHANCING'FREQUENGYL 1 TCONVERSION METHOD l 1 Q rescues-Myers; Wake foreskino. 1 J t V @ApplicatiomSeptember 1, 1943, Serial No. 500,781,

' 1 "fifcl iims (c1. 250-20) (Granted i'uhder the act '0: March 3,1883, as

aniende'dflpril 30, 11928;}370 0.13. my

invention relates to a signal enhancer andpr'imarily tomean'sand methods of inc-reasing""the amplitude and equency"sensitivity "of electric -wav cstectqrs;

'In conventional heterodyne detector's j i't ls ceiiin onto choose the frequensymr of the local or"heterodyiie frequency oscil1ato'r equal to the input signal (1) plus or minus the detector output frequency (f). Thus, in such circumstances, if twoinput signals are supplied to the input semifinals, *wmcnsienms 'aresepa i'ated e e par ticular nuinberof cycles (A?) ,"the output '"signals will-also "be 'separated 'by the same number of cycles.

conventicnars'ystem "ju'st described is not satisfactory in some appl'i'c'ation's andit is often fbund verydesirable-"tb effect 2. further differenti'ati'on-dr separation between wanted and "un wanted signals. "'I-heiiresent invention isde-' si'gnedto accomplish this by" increasing such diffeience frequency '(-Af;) such that the output'sig iials "are separated by --some integer multiple (greasemam) 'ofthe difference frequency, hf. This obviously enables the wanted and unwant edsignalsto be more easily distinguished or separated by some conventional -means, such as a fiitei miditi'ohal-ly, t

r'e "some applications, as

for-examine, sound engine *systemswhei'e-it is of' 'utmost importance to distinguish easily and positivelybetweenf two[sinalslwhose frequencies lie close tiig'ether 'although such frequencies may or'tnay not be in the receiyer simultaneously;

For instance, :in such systems, relative mbve' men't ofthe projector "and target causes tlie received frequency to be shifted by some 'small amount withrespeotto the'tfansmitted-frequency by virtue of the well known-D'opplereffect. Thus, depending upon whether the distance between projector and target is increasing or decreasing. the echo frequency will be lower or higher than the transmitted frequency. Since this Doppler shift may bevery-small means for increasing it.proves most valuable in its identification. e V Th invention is also so arranged that ampli- 'tude differences between signals are likewise increased'by yirtue thepower lawin a relationship Tfirb'dubd' "the "fact that the 'aln'plit'u'd or the out sut at 'a ei'ven frequency is 'preportional to I a power or the meet cofrespondiiigjtc theo'rdei 6f the 'fi'equ'ericy'differefioe multiplit i in gee-eras these advantages are accempnsuec byflusing e- -uete' or compr sing configuration of 'n'on-flineai elements, balanced in such a man; up: that the output contains =-substanna11y nc;

e be restricted ts heats" between E and f where F is the frequency of the local oscillator.

i course, may notbe? necessary where on1y -onei1i--" put signal is of interest ,-as.-wi ll be shown. In any case, the invention=-is practiced most simply by choosing the frequency -F of the local oscillator at n times (where nequals some intege g.

other tha'n ti e-frequency efth ih'pursierlei 1; plus osrfimusthe desired "output frequency; it. Very substanuai "im' iroveinentsin dperatienof the detector wn ijta e plsse becauseithe outputer t s 1oss1 oscillator 'b'e'ats' with the nth harmonic difference frequency A) by bvijously, such sepsis-mea s 0 we a "istancsm seutifie hc identifying-the desiredffrehuency.

n'tne drawin s: s Pieces 1 is a ci sfnsuc swingersSeaman gu re z i aschefi atic drawing srsnotiisr raim of the "iiiyention wmsn' mayjbs used tdificfeaise selectivitybetweentwo input sinals Figure ej s aschematic dra ing rsnnja other ee era epeu uon of *the'i'nvention whicli ma be s dmaupeses. I I

p eraficn or the in" 'ntic aesjc'riba-atb is can test he jexpis'i'nsa mathemat any. stanc, it cane jil ybe' sho" thatdetector o put freq neies rs) can be Trp'resented by the; roncwinegenerai equ t on; i I

comes e lt"=Fn7 62)" wher n-is-some integer greater' th an 1-.- "Min-1' Equation -2 it is immediately apparent that i-fthe input frequency ,f is increased by an amount 7'", the new output frequency fo' for such iniiut is given by the equation input'frequency change.

.Substituting from Equation 1 Thus. an increase in the inputfrequency in an amount jAf'lcausesf an increase in; output frequency ofan"amount nAf.

For example, suppose that it is desired to double y;

the frequency difference between two signals; and

' further, that when the input signal ;is'- equal/tow 20 kc., an 800 cycle audio beat is wanted atthe output. Then by Equation 2, the local oscillator 3 frequency (in kc.) is I F=foI fT should change by 200 cycles so that the new input frequency equalled 20,2; kc'.. thenew output fre:

only ;2 kc.,'theoutput signal increased by twice that amounhor .4 kc. Similarly, it may be shown that if i; by

a riount3, 4, 5. n times the amount of A. more'fcomplete mathematical analyf ls lofj effects which are madepse of in the present i n;

vention is included in 'Everitts Communication Engineering,,Chap. XIII. For example onpage 379"Everitt states, .when 'onlytermsup to h s a e ne n Tarlb i jse e e eac p tance',jthe sum and difference frequencies ;in. the

output" have intensities which-are, proportional;

tg theproduct of the intensities of the two frequencies'that produce them. Similarly it isapparent from a study of an expansion-ot'laylors e es h h mo ul tionf equenc e i h utpu'tfhave intensities proportional ;to the products off, the frequencies "that produce them. 3 This is statediasjthe' Fundamental Principle of Modulationin Evritt (page 393) and treated through out the remainder of Chapter XIII with respect to higher order modulation a'nddemodulation prod- ;jFromthe'same reference, it will be ,cleanthat the amplitude of the output signal will be proportional to .the nth power of the'desired input signaL'where n is de nes, described above Thu where' fnis chosen as 2 the outputamplitudewill be pro'portional to the inputlamplitude squared.

when n' is 3, it will be proportional to the input amplitude cubed, etc. Thus, in addition to the. desirable ir'equency effects the invention provides a convenient means for .distinguishingrthe" desired signal by virtue of the power law. char-, acteristic ofthe amplitude. For example, if. the ratio of the amplitudes of the incoming desired andgundes iredsignal is r, the corresponding ratio in the output will be equal to r".

In echo-ranging applications, noticeable improvement in the signal't noise (reverberation) ratio may wellfibe dueto this latter effect; If it beassumed, for. instance, that 4 reverberation is madeaup ofmanyfrequencies, each of which has I a; f ractional amplitude as compared with the am-' plitude of the signal, the effect is t'oreduce eachfrequency componentbythe nth power of its original fractional amplitude: hlthough the root mean square value 'ofthe original reverberation Thus,[although the input signalincreased is taken equal to any integer as 3, 4, the output frequency will be changed .ventional type of detector can be utilized, as will bobvious to those skilled in the art. I

iwithieference to.the various circuit arrangements;- several typical ones of which are illustrated-inthe drawings, it can be said that in all case'sthe local oscillator frequency (which is made 'lnearlyleqiialto some integral multiple of the in- Under these circumstances, if itheinp'ut sig nal."

.tp i s co dens .iandi wame e d -5 This particularicircuit may gnotebe utilized for put frequency) beats with the corresponding harmonic of the input frequency to produce the desired output-frequency, In some circuit arrangements', it is foundthat both odd and even multiples can be utilized in the same circuit; while in others, -it may be found that operation can be obtainedcnly with, odd or even multiples. For any, particular application, the circuit 'mustibe chosen such that thedesired multiplei'sobtained. .5. g It should also be noted that a'lftli'ough sorne' I cuits discrirninate against ,Ijiarticular iml iltip Q5,

s anst be userl e eithe ss fiiri i i 'i is not perfect, thecirouits'normallyno be' actly balanced. .yy 1

One form of the invention i'sg sliown iriFi'gin'which a single-elementdetector .l is conne in series with input terminals} and local 1o later-terminals 3 The output is talgen of f acro s resistor 4 and filtered by'means of the filter, co

plied at terminals 1. The purpose of the filter is to insure supplying-only the difference frequ'e cies toterminals most applications asd scribed, thiswillbe an audio ,irequency qi E'- pa t on of 1 wo i put. f qu e est u Srvii quitesatisiactorily for applications such as was? describedwi h resp t .to h p le ie ie t-r ns echo ranging lgear. I

Fi u al i lu t an t er P0 51 6 a p ca ion;

' in which twov input signalsjmay be separated, but;

only if n is chosen as some odd integer. Here; two detectors {5, 9 areused, connected inthe manerxp a-fu l-wave -r..ec fie .i i hwth i p t 5 121 plied across inductance H1 at terminals. H. The;

" localsoscillatorterminals '1 2 are. conne'ctedin se;=

ries with resistor l5 and the, output is takenoutf at terminals {4. across suchres istor,- capacitor= l3 .providing;a low. impedance path, for tl rsig-g nal frequencies and-servingthe samepurposeas;

. creased only by 1; 3-, 5;7, etci times- L the filter in Fig. l; This arrangement; will not, operate effectively, as .has been said,: Wheren is an eveninteger, sothat it will, enable the diiference frequencyhbetween' input signals; to be in-.

-If itis desired to have one'circ'uit performundei" all'conditions, where n'is eithroddor even, the

balanced configuration of non-linear elein e nts shown in Fig. 3 is-v'ery convenient. Here'four 5:.- elements, [6, l1, l8,'-- |9 are connectedtoiorm-a hat b ho en.less h iofl .his na ic a CQPPBI- rQxideMed lst sbalanced-detector. The input andflocal 'osc1'llator frequencies are supplied at terminals respectively, at oppositecorners ofth'eibalanced configuration, and the output is'suppliedtoter-j minals ZZ, after having been filtered bythei ilte'r,

comprisingdnductance 23 "and capacitoffli In this circuit, bothodd and even harmcn ics o input beat with the local oscillator frequen ames? The Bell Telephone Systems, by R. S. Caruthers,

System Technical Journal, April 1939, pages 315- 317.

In all of the above cases, the filter circuits are chosen as illustrative and any other conventional arrangement may be used.

In most cases the choice of position of the invention in the existing sound-ranging or other equipment is one of convenience. It may be arranged as a supplement to the existing units with the detector and oscillator operating on the signal before it is fed into the receiver, or incorporated into it by simply altering the frequency of beat frequency oscillators which are a part of the present systems.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

Having described my invention, I claim:

1. A method of enhancing the frequency deviation of a signal frequency comprising the steps of receiving said signal frequency, generating a fixed frequency differing by a preselected output frequency from an integral multiple greater than one of said signal frequency, mixing the signal frequency and said fixed frequency and deriving said preselected output frequency, said output frequency having a frequency deviation corresponding to that of the received signal multiplied by an amount equal tothe integral multiple selected for use.

2. In the method described. in claim 1, said integral multiple taken equal to 2 and said preselected output frequency being an audio frequency.

3. A method of signal selection comprising the steps of receiving two input signals of different frequencies, generating a fixed frequency differing by a preselected output frequency from an integral multiple greater than one of a first of said signal frequencies, mixing the two signal frequencies and the fixed frequency and deriving said preselected output frequency, said output frequency having a frequency deviation corresponding to that of said first input signal multiplied by an amount equal to the integral multiple selected for use.

4. In the method described in claim 3, said integral multiple taken equal to two, and said preselected output frequency being an audio frequency.

5. A method of signal selection comprising the steps of receiving a plurality of signals of different frequencies, generating a fixed frequency a differing by a preselected output frequency from an integral multiple greater than one of a first of said signal frequencies, mixing the signal frequencies and the fixed frequency, and selecting said preselected output frequency corresponding to said first signal frequency while rejecting the output frequencies corresponding to the others of said plurality of signals, said plurality of output frequencies differing by an amount equal to the difference between the corresponding input signals multiplied by said integral multiple.

6. A method of enchancing the selective properties of a transducer comprising the steps of receiving a signal frequency, generating a fixed frequency differing by a preselected output frequency from an integral multiple greater than one of said signal frequency, mixing the received signal frequency and the fixed frequency, and deriving an output signal of said preselected frequency having an amplitude which is related to the amplitude of the corresponding input signal in accordance with an exponential law of order corresponding to said integral multiple.

7. A method of signal selection comprising the steps of receiving a plurality of signals of different frequencies of slightly differing amplitudes, generating a fixed frequency differing by a preselected output frequency from an integral multiple greater than one of a first of said signal frequencies, mixing the signal frequencies and the fixed frequency and selecting the output signal of said preselected frequency corresponding to said first signal frequency while rejecting the output signals corresponding to the other signal frequencies, said output signals having an amplitude difference which is greater than said amplitude difference of said input signals.

JACO'B C. MYERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,420,055 Nichols June 20, 1922 1,699,570 Potter Jan. 22, 1929 1,802,760 Gage Apr. 28, 1931 1,813,923 Heising July 14, 1931 1,920,238 Black Aug. 1, 1933 2,086,601 Caruthers July 13, 1937 2,140,526 Haffcke Dec. 20, 1938 OTHER REFERENCES Everitt: Communication Engineering (2nd edition), 1937, pages 398-403. (Copy in Div. 51.) 

